The medial amygdala posterior dorsal (MEApd) and principal nucleus of the bed nucleus of the stria terminalis (BSTpr) are thought to be critical for integrating hormonal and olfactory signals and modulating reproductive behavior accordingly. Our long term goal is to elucidate the connectivity and function of genetically defined MEApd and BSTpr neuronal subpopulations in order to determine the specific circuits and mechanisms responsible for translating hormonal and chemosensory inputs into specific behavioral outputs. The specific hypothesis to be tested in this proposal is that MEApd and BSTpr contain multiple functionally distinct neuronal subpopulations, each of which make essential but unique contributions to reproductive behavior. This hypothesis will be tested via the following three specific aims: 1) Use classical neuroanatomical tracing to determine if multiple neuronal subpopulations with distinct connectivity exist in MEApd and BSTpr; 2) Determine if MEApd receives input from both the AOB and MOB using Cre-dependent transneuronal tracers; 3) Use genetic ablations to test the hypothesis that distinct MEApd and BSTpr neuronal subpopulations serve unique functional roles in modulating male reproductive behavior.